LEIRVEGILIAUCHAIL, WAUILILIB VES (OIF WIGHE, IO SSH SSILPUAM 751 
The Illinois Valley —The data concerning the rock floor from 
the bend of the Illinois northward, along the preglacial valley 
are very meager. Professor Chamberlin reports a boring at 
Lake Koshkonong, Wisconsin, which failed to reach rock at 450. 
feet. A. T. A boring at Janesville, Wisconsin, enters rock at 530 
feet A. T. and several at Rockford, Illinois, at 529-588 feet A. T. 
But these are all very near the west bluff and, in all probability, 
enter rock much above the level of the deepest part of the old 
channel. It is in the portion of the old valley occupied by the 
Illinois that the rock floor is best known. 
We begin the table at the head of the present Illinois, 
that the contrast between the new and the old valley may 
be brought out. For the low water altitudes and for the 
measurement of distances we are indebted to a report of the 
Chicago Drainage Commission, prepared by Mr. L. E. Cooley, 
an engineer of that commission. Records of borings showing 
the elevation of the rock floor have been obtained at the offices 
of the persons or companies who made them, except in the case 
of the Princeton artesian well. The record of this well was fur- 
nished by Mr. Jacob Miller, President of the Princeton Academy 
of Science. The Princeton well-boring is here included, since it 
is near the border of the present Illinois Valley and probably 
strikes the deepest part of the old channel. We are indebted to 
EnoOrKessonn| Aq Uddeny lot Rock Island we ton the collectionor 
records of wells at Bureau Junction, Hennepin, Putnam and 
Henry. 
*It should be noted that the low water altitudes here given, taken from the report. 
of the Missouri River Commission, average about four feet higher than in Gannett’s. 
Dictionary of Altitudes, Bull. U.S. G. S., No. 76. The altitudes given in the table 
for the Mississippi are from Gannett’s Dictionary of Altitudes. 
? The report of the Missouri River Commission for 1890 contains a description of 
a gorge 2000 feet or less in width and 60-75 feet in depth, which crosses the valley in 
an east to west direction, nearly at right angles with its present course. 
3 The river silts and sands extend only to elevation 790 feet. Beneath them is a. 
hard clay seventy-five feet in depth. The description given in the reports of the Mis- 
sourl Commission do not make clear whether it is a glacial deposit or an earlier 
formation. 
